Elimination of viscous drag in a magnetic fluid clutch



Feb. 13, 1951 D c PRINCE 2,541,831

ELIMINATION OF VISCOUS DRAG IN A MAGNETIC FLUID CLUTCH Filed May 7 1949LS 43 IO I6 39 47 2 8 T 9 4 ll 2 58 5 k 30 4 l5 Inventor: Davlcl CPrmce,

His Attorney.

Patented Feb. 13, 1951 ELIMINATION OF VISCOUS DRAG IN A MAGNETIC FLUIDCLUTCH David 0. Prince, Schenectady, N. Y., assignor to General ElectricCompany, a corporation of New York Application May 7, 1949, Serial No.92,042

1 Claim.

My invention relates generally to magnetic fluid clutches and moreparticularly to an improved arrangement for the elimination of viscousdrag therein when such clutches are operated in the released ordisengaged condition.

In power-transmitting clutches of the magnetic fluid type,finely-divided particles of a magnetic material such as iron aresuspended in a fluid such as oil, and the resultant mixture is caused,by virtue of a magnetic field acting thereon, to create a drag between apair of rotatable members or plates. While the creation of such amagnetic fluid drag is the normal function of a clutch of the typementioned when the clutch is energized or "engaged" for normalpowertransmitting operation, it is frequently desirable to operate theclutch in the deenergized or disengaged condition, that is, without thepresence of a magnetic field, so that the power-transmitting effectthereof is greatly reduced. Under such condition, while the effect ofmagnetic fluid drag is absent, the clutch may still function to anappreciable extent in the manner of a conventional fluid clutch byvirtue of the presence of viscous drag between the clutch elements, dueto the presence of the fluid mixture in the clutch chamber. a

The presence of viscous drag may be undesirable in many applications,since the clutch is not truly disengaged even when a magnetic field isnot present. An appreciable amount of torque may be transmitted by theclutch which may cause "creeping" of a load connected thereto. Moreover,such viscous drag may cause appreciable power losses which serve nouseful purpose. In many applications, magnetic fluid clutches are atpresent altogether unsuitable because of continuing losses due toviscous drag. This is particularly true with respect to small clutchesoperating at high speed in an application such as a reversing gearwherein a drive operates during a large portion of the total time withone clutch fully engaged and the other completely disengaged. A furtherlimitation imposed on clutch design by, the presence of viscous draglies in choice of a suitable gap dimension between the magneticrotatable members of a clutch, to secure high operating torque andefflciency when the clutch is engaged without accompanying excessiveviscous drag torque when the clutch is disengaged.

Accordingly, it is the principal object of my invention to provide animprovement in clutches of the magnetic fluid type, whereby viscous dragmay be wholly eliminated therein when such clutches are operated in adisengaged condition.

In its broadest aspect, my invention provides for removal of the fluidmixture from the vicinity of the clutch plates when the clutch isdisengaged, thereby eliminating viscous drag by virtue of the absence ofa viscous medium. In particular, in a preferred embodiment of myinvention hereinafter described, I provide an auxiliary reservoirconnected to the main ,clutch chamber, and having a sufficient capacityto contain the entire fluid mixture normally contained in the mainchamber when the clutch is engaged. The flow of the fluid from theclutch chamber to the reservoir or vice versa, is effected by the actionon the fluid of centrifugal or suction forces associated with therotational motion of the clutch, and such flow is controlled by the useof a suitable valve.

For a better understanding of my invention. together with other objectsand advantages thereof, attention is now directed to the followingdescription and the single figure of the accompanying drawing, wherein aclutch of the magnetic fluid type, including a preferred embodiment ofmy invention, is represented.

Referring now to the drawing, there is shown a power-transmitting clutchof the magnetic fluid type having the principal elements thereofcontained in a housing I, from which protrudes a pair of shafts 2 and 3,either of which may serve as a power input shaft while the other servesas a power output shaft. Housing l comprises a generally cylindricalhollow center portion 6, a hollow auxiliary portion 5 eccentricallypositioned with respect to center portion 4, and a pair of cylindricalhub portions 6 and l coaxially positioned with respect to center portion4 at the ends thereof. Hubs 6 and 1 are arranged to accommodate a pairof bearings t and 9, respectively, which support shafts 2 and 3. Shaft 2is restrained from axial motion by a pair of suitable collars H) and IIwhich are maintained in fixed relation with shaft 2 by suitablefastening devices such as set-screws i2 and I3.

Housing I is represented as having a relatively large chamber 14 withincenter portion 4, and a smaller chamber 15 adjacent to and coaxial withchamber I4, but contained within hub portion 5. Shaft 2 extends throughchamber [5 into chamber M and terminates therewithin. Shaft 3 likewiseextends into and terminates within chamber l4, and is restrained fromaxial motion in the direction thereof by a collar i6 maintained in fixedrelation with shaft 3 by a set-screw ll.

It will be understood that while housing I may be considered as anintegral unit, it is preferably constructed in two or more sections tofacilitate manufacture thereof and assembly of other clutch elementstherewith. In the illustrated embodiment housing I, which is formed of anon-magnetic material, preferably metal, is represented as comprising aduality of sections which may be conveniently designated as a bodyportion l8 and a cover portion l9. Body I8 and cover I9 are joined at amating surface and are maintained in clamping engagement by a series ofbolts 2| spaced about the peripheries of body I8 and cover I9. Body I8and cover l9 are maintained in coaxial relationship by a rabbet 22having a gasket 23 clamped therein to render joining suria"e 20 tightagainst fluid leakage.

A clutch member 24, having a plate portion 25 and a hub portion 26, iscarried by shaft 2 and is positioned at the end thereof within chamberI4, and is maintained in fixed relation with shaft 2 by a suitablefastening device such as a setscrew 27. A second clutch member 28,having a plate portion 29 and a hub portion 38 is carried by shaft 3 andis positioned at the end thereof within chamber I4, and is maintained infixed relation with shaft 3 by set-screw 3|. Shaft 3, restrained fromaxial motion in the direction of chamber I4 by collar I6, is similarlyrestrained from motion in the opposite direction by hub 38'. Members 24and 28 are positioned on shafts 2 and 3, respectively, in a manner toestablish a suitable fixed gap distance 32 between faces 33 and 34.

Plates 25 and 29 are formed of a magnetic material such as iron. Plate29 is provided with a magnetic winding which is represented as anannular winding 35 coaxially positioned with respect to plate 29 in acylindrical recess 36 thereof. Recess 38 is covered by an annular plate31 formed of a non-magnetic material, preferably metal. Winding 35 isconnected by a pair of conductors 38 and 39, positioned in a passage 40which is drilled or otherwise formed in shaft 3, to a pair of slip rings4| and 42 fixed on shaft 3 outside housing I and insulated from eachother and from shaft 3 by an insulating member 43. Slip rings 4| and 42are connected through a pair of brushes 44 and 45 and a switch 46, to asuitable source of unidirectional potential such as battery 41.

Auxiliary portion 5 is represented as having a chamber 48 connected withchamber I4 in center portion 4 by a relatively large passage 49 at theperiphery thereof. Chamber 48 is connected with chamber I5 in hub 6 by arelatively small passage 58 in the periphery thereof. While no provisionis made for closing passage 49, provision is made to open or closepassage 50 by the use of a valve mechanism 5| supported in a bossportion 52 of auxiliary portion 5, and arranged to be externallyoperable withrespect thereto. In particular, passage 50 is representedas being a tapered hole which may form a seat for valve mechanism 5|.Valve 5| is represented as comprising a tapered plug portion 53 arrangedto mate with opening 50, a stem 54 attached to plug 53, an externallythreaded rod 55 attached to stem 54, and a suitable handwheel 58attached to threaded rod 55. Plug 53, stem 54, rod 55, and handwheel 56are attached to one another in fixed rotational relation, so thatrotation of handwheel 58 causes corresponding rotation of plug 53.Threaded rod 55 is threadedly engaged in an internally threaded sleeve51 which is secured in fixed relation with respect to boss 52. Thus,rotation of handwheel 88 and plug 53 causes axial motion thereof, inturn causing opening or closing of passage 50 according to the sense ofrotation of mechanism 5|.

In connection with the clutch member 24 and chambers I4 and I5, it willbe noted that a sealing wall 58 is provided around hub 26 betweenchambers I4 and I5 in the form of a ring integral with body I8 ofhousing I. Wall 58 is arranged to fit closely about the periphery of hubI5, to prevent any appreciable flow of fluid therealong between chambersI4 and I5. Further, a plurality of tubular passageways 59 are providedin member 24 extending through hub 28 and plate 25 thereof, andinterconnecting ch'amber I5 and gap 32.

In considering the operation of the clutch herein illustrated, it isassumed that shaft 2 is connected to a suitable source of drivingtorque, such as a motor (not shown), and that shaft 3 is simlarlyconnected to a load device (not shown), the latter being driven throughthe clutch by coupling action between clutch members 24 and 28. Suchcoupling action is provided by the use of a fluid mixture, designated inthe drawing by numeral 60, comprising a relatively viscous fluid, suchas oil, and finely-divided particles of a magnetic material, such asiron, suspended therein.

If it be assumed momentarily that chamber I4 is closed, or in otherwords that chambers l4 and 48 are not connected by passage 49, and thatpassage 58 is closed by plug 53, thereby isolating chamber 48 fromchamber I5, the operation of the clutch may be first considered withoutregard to auxiliary chamber 48.

In normal operation of the clutch, fluid mixture 60 is contained in theinterstices of chamber I4 surrounding clutch members 24 and 28 and, inparticular, in gap 32 therebetween. If switch 48 is closed, a current iscirculated through Winding 35 and a magnetic field is created thereby inplates 25 and 29. In particular, the magnetic field thus created passesthrough gap 32 between plates 25 and 29 and also through that portion offluid mixture 80 contained therebetween. The finely-divided particles ofmagnetic material suspended in mixture 80 are caused by the magneticfield passing therethrough to cling together and also to cling tosurfaces 33 and 34 of plates 25 and 29. The clinging action thuseffected causes a drag to be created between clutch members 24 and 28when the former is rotated by the driving source connected to shaft 2,and thus a torque may be transmitted through the clutch to the loaddevice connected to shaft 3. Under this condition, the clutch isengaged.

If it is desired to disengage the clutch, switch 46 is opened and thecircuit of winding 35 is broken. thereby causing the magnetic fieldassociated therewith to be reduced to substantially zero. The tendencyof the finely-divided particles in mixture 60 to cling together and tocling to faces 33 and 34 is likewise reduced to substantially zero.Underthis condition, no torque, due to magnetic action on fluid mixture80, is transmitted by the clutch. However, due to the presence of aviscous medium in the vicinity of clutch members 24 and 28, anappreciable amount of torque may be transmitted by the clutch due toviscous drag, in the manner of a conventional fluid clutch. Aspreviously noted, the presence of such torque may be undesirable in manyapplications. According to my invention, I provide for the completeelimination of such torque by removal of the viscous medium, representedin the illustrated embodiment by fluid mixture 60. from the vicinity ofclutch members 24 and 28 when the clutch is disengaged.

It is now assumed that main clutch chamber [4 and auxiliary chamber 48are interconnected by passage 49, as previously described and as shownin the drawing, and that fluid mixture 60 is contained in chamber l4. Itis further assumed that switch 46 is closed and that torque is beingtransmitted through the clutch by virtue of magnetic action on fluidmixture 80, as previously described. In other words, the portion ofmixture 60 contained in gap 32 between faces 33 and 34 may be consideredto be frozen" and, accordingly, to have no appreciable tendency to flow.If the clutch is now disengaged by de-energizing winding 35, mixture 60,due to the reduction of the magnetic field to substantially zero, is nolonger frozen but is substantially liquid in form and may easily becaused to flow by centrifugal forces present in rotating members 24 and28. There is, accordingly, a tendency for mixture 60 to be thrown out ofgap 32 and to accumulate at the periphery of chamber l4.

By suitable design, mixture 60 may be caused to pass through opening 49into chamber 48 and to accumulate therein, chamber 48 thereby performingthe function of a reservoir. To cause such accumulation, passage 50 maybe closed by manipulation of handwheel 56 and valve mechanism 5|. Thus,in a short time, fluid mixture 60, previously contained in chamber I4,is completely thrown out of chamber l4 into reservoir chamber 48,leaving no viscous medium in chamber l4 to cause viscous drag in thedisengaged clutch.

If it is now desired to re-engage the clutch, passage 50 may be openedby manipulation of hand-wheel 5B and valve mechanism 5|, permitting theflow of mixture 50 contained in chamber 48 through passage 50 intochamber l5, by virtue of forces of gravity acting on mixture 60. Aschamber I5 is filled by mixture 60, a pressure is created thereintending to force mixture 60 through tubular passageways 59 in clutchmember 24 and thence into gap 32. Centrifugal forces in gap 32 tend tothrow mixture 60 outward, in turn creating suction forces in passages 59which tend to maintain a flow of mixture 60 through passages 59, evenafter chamber 48 is emptied and a fluid head no longer exists therein.If a magnetic field is not established between plates and 29, the flowof fluid mixture 50 continues and mixture 60 is again thrown intochamber 48 and a continual recirculation occurs. However, when asufiicient time has elapsed following opening of passage 50 to permit asubstantial portion of mixture 60 to be contained in gap 32, switch 46may be closed, causing the mixture 60 in gap 32 to be frozen by magneticaction. Thus, normal power-transmitting action of the clutch may beresumed. It is desirable to close passage 50 following engagement of theclutch to permit the surplus of mixture 60 surrounding clutch members 24and 28 in chamber l4 but not contained in gap 32, to be thrown out ofchamber It and to be accumulated in chamber 48, thereby reducing theviscous drag While the details of operation described are useful inunderstanding my invention, it will be understood that in the practicalapplication of my invention, when it is desired to engage the clutchsuch an operation involves only manipulating handwheel 56 to its openposition and, after a suitable time, closing switch 46, whereuponhandwheel 56 is preferably manipulated to its closed position onceagain. Disengagement of the clutch then involves only opening switch 46.The functions of removing mixture 60 from chamber I 4 and returningmixture 60 once again to chamber l4 are accomplished automatically inthe illustrated embodiment by making use of centrifugal and gravityforces and the like associated with the clutch mechanism.

While I have shown a preferred embodiment of my invention, I wish topoint out that the application of my invention is not necessarilylimited thereto and variations thereof will undoubtedly occur to thoseskilled in the art. For example, while the valve mechanism 5| is hereinrepresented as being manually operable, it is readily apparent thatvalve mechanism 5| could equally well be actuated remotely by a solenoidor the like. I aim, therefore, in the appended claim, to cover all suchchanges and modifications as fall within the true spirit and scope of myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

In a clutch of the magnetic fluid mixture type a housing defining anoperating chamber and a storage chamber separated by a common wall witheach chamber suitable for housing a magnetic fluid mixture. a pair ofrotatabl soft iron clutch members positioned in said operating chamberand spaced apart in parallel juxtaposition to define a gap, meansincluding an electrical circuit for transmitting torque from one of saidclutch members to the other b energizing said circuit to pass a magneticfield through said fluid in said gap, said common wall defining withsaid housing a passageway at the top of said operating chamber forconducting said magnetic fluid mixture by centrifugal forc from saidoperating chamber to said storage chamber when said electrical circuit ide-energized, a valve positioned between said storage chamber and saidoperating chamber, and means for opening said valve to conduct saidmagnetic fluid from said storag chamber to said operating chamber.

DAVID C. PRINCE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,182,049 Henry Dec. 5, 1939FOREIGN PATENTS Number Country Date 448,977 Germany Sept. 1, 1927794,008 France Feb. 6, 1936 OTHER REFERENCES Bureau of StandardsTechnical Report 1213. received in Div. 68, Mar. 30, 1948, 192-MFN.

